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Conventionally, sound insulation materials have been applied to control interior noise above 500 Hz, and damping materials to control interior noise below 500 Hz. In this paper, the noise control component for vehicle panels, which consists of damping material and sound insulation material, is investigated by using a two-degrees-of-freedom system. The investigation shows that sound insulation material can be effective in reducing interior noise below 500 Hz if its stiffness is reduced. This stiffness depends not only on the spring of the material itself but also on its pneumatic spring which is determined by air-flow resistance. This paper concludes with applications of techniques to reduce interior noise below 500 Hz by improving sound insulation materials.

In order to reduce the interior noise of a vehicle with a four-cylinder engine, investigations were made using finite element and vector methods, acoustic intensity testing and holography technique. The investigation resulted in inclination of the engine mounting, design changes to the front suspension member, a shock absorber engine mounting, structural modifications to reduce body panel vibration and a new engine mounting to insulate high frequency engine vibration.

A reliable finite element model (FE model) for the suspension of front-engine front-wheel-drive vehicles (FF vehicle) was developed. The model allows analysis which clarifies the role of each suspension component for road noise reduction in the 130- 160 Hz range. To analyze road noise up to 200 Hz, an accurate suspension FE model including tire FE model was developed. All suspension components are modeled in detail by shell or solid element. This saves the validation of model and enables us to use it early in the design stage. To save calculation time, some suspension components in which structure is not a concern are transformed into modal model. To acknowledge each subsystem's role to the entire suspension system a new approach was introduced. In this approach, important internal forces between subsystems are selected. These internal forces have high contribution to transmissibility forces at the body attachment point (body transmissibility force).